Ambient temperature compensated circuit breaker



NOV. 26, 1968 MaCDQNALD 3,413,581

AMBIENT TEMPERATURE COMPENSATED CIRCUIT BREAKER Filed Oct. 5, 1966 2 Sheets-Sheet 2 IN VE N 7 OR.

United States Patent 3,413,581 AMBIENT TEMPERATURE COMPENSATED CIRCUIT BREAKER John MacDonald, .lackson, Mich, assignor to Mechanical Products, Inc., Jackson, Mich., a corporation of Delaware Filed Oct. 5, 1966, Ser. No. 584,484 6 Claims. (Cl. 337-39) This invention relates generally to electric circuit breakers, and more particularly to an improved trip device for an electric circuit breaker.

Automatic electric circuit breakers generally comprise a pair of separable contacts, an operating mechanism that is releasable to effect separation of the contacts, and a trip device responsive to predetermined electrical conditions in an electrical circuit to effect release of the operating mechanism. Generally, the trip device comprises a latch mechanism and a current responsive element that effects movement of the latch mechanism to a release condition.

It has long been a problem to produce a relatively inexpensive and compact trip device for a circuit breaker of relatively low current rating that is properly compensated for changes in ambient temperature, particularly large changes in ambient temperature, and that will at the same time be sufficiently sensitive to relatively small overloads.

In accordance with the present invention, an improved trip device for a circuit breaker is provided that is properly compensated for changes in ambient temperature. This is accomplished by mounting an operating mechanism that pivotally carries a latch having a movable contact mounted thereon in a circuit breaker housing for a limited degree of transverse movement with respect to the normal axial movement of the operating mechanism. The operating mechanism is suitably coupled to an ambient temperature compensating means that will move the latch in the same direction as a latching surface mounted on a current responsive member in response to changes in ambient temperature. This means preferably comprises a bimetal member attached to the housing and coupled to the operating mechanism, with the current responsive member also comprising a bimetallic member attached to the housing and having a free end with a latching surface thereon that engages the latch positioned on the operating mechanism.

An object of the present invention is the provision of an improved trip device for a circuit breaker that is properly compensated for changes in ambient temperature, particularly very high changes in ambient temperature.

Other objects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a longitudinal sectional view of the circuit breaker of the present invention;

FIG. 2 is a longitudinal sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is a cross sectional view taken substantially along the lines 3-3 of FIG. 1; and

FIG. 4 is a cross sectional View taken substantially along the lines 4-4 of FIG. 1.

As best seen in FIG. 1 of the drawings, an electric circuit breaker comprises an insulating housing 12 molded from, for example, Bakelite. A pair of terminals 14 and 16 extend from the housing for connection to opposite sides of an external circuit.

The terminal 16 extends inwardly of the housing 12 for the support of a fixed contact 20. A movable contact 22 is aligned and engageable with fixed contact 20 to complete an electric circuit through the circuit breaker 10 comprising the terminal 16, the fixed and movable contacts 20 and 22, a pigtail 24, a current-responsive trip device generally designated by the numeral 26, a pigtail 28 and the opposite terminal 14.

The operating mechanism for the circuit breaker 10 comprises a manual operator 29 that extends externally of and is slidably positioned in the housing 12 for axial in-and-out movement. The manual operator 29 comprises a plunger portion 30 having an upper end 31 that extends into a guideway 32 formed in an upper wall 34 of the housing 12. The central portion of the plunger portion 30 extends through a slot or aperture 35 formed in the lower wall 36 of the housing 12. The guideway 32 formed in the upper wall 34 and the aperture 35 formed in the lower wall 36 provide suflicient clearance between the housing 12 and the plunger portion 30 to permit a limited amount of movement in a direction transverse to the normal axial in-and-out movement of the manual operator 29.

The outer portion 37 of the manual operator 29 extends through a ferrule 38 positioned in the lower wall 36 of the housing 12 and it has a knob 40 secured thereto as by a pin 41. The knob 40 is preferably formed of an insulated material, for example, Bakelite and is shaped to facilitate manual operation of the circuit breaker 10.

The plunger portion 30 of the manual operator 29 is normally urged outwardly of the housing 12 by a helical compression spring 42 positioned in a complementary spring recess 44 formed in a spring housing 45 that is in engagement with the knob 40. This spring 42 engages this housing at one end and the lower wall 36 of the housing 12 at the other end.

The plunger portion 30 of the manual operator 29 is also normally resiliently urged outwardly of the housing 12 by a tensioned coil spring 47 having one end portion 48 secured to a bracket 51 on a contact carrier 52. The other end portion 53 of the spring 47 is connected to a transversely extending bracket 54 integrally formed with a resilient L-shaped cam member 55 which has one leg secured to the lower wall 36 of the housing 12 by rivets or other suitable fastening means 56. The other leg has a camming surface 57 positioned thereon, and this camming surface 57 is positioned in engagement with a canted cam follower surface 58 on a follower 59 carried by the plunger portion 30 of the manual operator 29 by means to be described subsequently.

The spring 47 is sufliciently strong so that when it is tensioned to the position illustrated in FIG. 1 it holds the camming surface 57 in engagement with the canted cam follower surface 58 thereby restraining the plunger portion 30 of the manual operator 29 from movement outwardly of the housing 12 under the bias of the helical spring 42.

However, when the tension of the spring 47 is relieved upon the automatic opening of the circuit breaker 10, as will be described, the spring 42 is sufficiently strong to bias the plunger portion 30 of the manual operator 29 downwardly thereby moving the camming surface 57 transversely to the left as shown in FIG. 1 so that it engages the vertical side of the cam follower 59. This permits continued outward movement of the plunger portion 30 and the manual operator 29 under the bias of the operating spring 42. Similarly, movement of the camming surface 57 of the resilient cam member 55 outwardly into engagement with the vertical surface of the cam follower 58 is also effected upon downward movement of the plunger portion 30 of the manual operator 29 upon manual operation of the circuit breaker 10.

The contact carrier 52 is pivotally supported by a pin 60 that extends through the plunger portion 30 of the manual operator 29 and also through bores in the cam tion and the pin 60 is received in cylindrical bearing structures 61 formed on the outer legs thereof. Furthermore, this pin 60 provides the attaching means for the cam follower 59 on the plunger portion 30 of the manual operator 29, with a small amount of lost motion provided by an enlarged bore or aperture 62 in the plunger portion 30. The contact carrier 52 has a latching surface 63 positioned thereon that underlies in coextensive relationship with a complementary latching surface 64 on the trip device 26 to be described.

Upon disengagement of the latching surfaces 63 and 64 on the contact carrier 52 and the trip device 26, respectively, the contact carrier 52 rotates counterclockwise under the bias of the spring 47 to carry the movable contact 22 out of engagement with the fixed contact 20 thereby breaking an electrical circuit through the circuit breaker 10.

In accordance with the instant invention, the trip device 26 comprises a resilient bimetallic member or blade 70 that has a pair of spaced legs 71 and and 71 secured to the lower wall 36 of the housing 12 by suitable fastening means, for example, rivets 69 and an upstanding leg 72. The upstanding leg 72 carries a block 73 that has the latching surface 64 positioned on the underside thereof. The pair of spaced legs 71 and 71 and the upstanding leg 72 are joined by a centrally curved portion 74 that will deflect under different temperatures to move the block 73 and latching surface 64 to the right as viewed in FIG. 1, as the result of increasing temperatures and to the left as viewed in FIG. 1 as the result of decreasing temperatures.

With the circuit breaker in its closed position as shown in FIG. 1, a current path is provided from the terminal 16 through fixed contact 20, movable contact 22, pigtail 24, the bimetal member 70, and the pigtail 28 to the terminal 14. Thus, current flows through the bimetal member 70 during the normal operations of the circuit breaker. If this current is below a predetermined level, the bimetal member 70 will maintain the latching surface 64 on the block 73 in engagement with the latching surface 63 on the contact carrier 52 thereby maintaining the circuit breaker in closed condition. If, however, current through the bimetal member 70 rises to a certain predetermined level at which the circuit breaker is designed to open, the heat generated by the current and the resistance of the bimetal will move the end 72 and the block 73 transversely to the right as shown in FIG. 1 thereby disengaging the latching surfaces 63 and 64. This permits the contact carrier 52 to rotate counterclockwise under the bias of spring 47 thereby bringing the fixed contact and the movable contact 22 out of engagement and breaking the circuit through the circuit breaker.

It can be readily appreciated that the bimetal member 70 will also deflect under ambient temperature. As ambient temperature rises, the block 73 and the latching surface 64 will be moved to the right as viewed in FIG. 1 and as ambient temperature falls, the block 73 and latch ing surface 64 will be moved to the left thereby affecting the operating point of the circuit breaker. Under high ambient temperature, the circuit breaker would be actuated at lower current levels than it would at lower ambient temperatures.

The present invention provides a novel ambient temperature compensating means generally indicated by the numeral 80 for maintaining the operating point substantially constant under a wide range of ambient temperature. This ambient temperature compensating means comprises a bimetal member or blade 81 having an upstanding leg 82 positioned in a plane generally parallel to the plane of the upstanding leg 72 of the bimetal member or blade 70. An inturned generally horizontal leg 83 of the bimetal member 81 is aflixed to the lower wall 36 of the housing 12 by any suitable fastening means, for example, rivets 84. An L-shaped bracket 94 has one leg 95 attached to the upstanding leg 82 of the bimetal member 81 and another inwardly extending leg 96 that has slot 97 positioned therein for the reception of the upper end 31 of the plunger portion 30. Thus, under changes in ambient conditions, the upper end 31 of the plunger portion 30 and hence the latching surface 63 positioned on the contact carrier 52 will be moved transversely to the left or right, as shown in FIG. 1, under the movement of the leg 82 of the bimetal member 81. In the case of increasing ambient temperature, the latching surface 63 will be moved to the right as viewed in FIG. 1 and under decreasing ambient temperature, it will be moved to the left. The bimetal members 70 and are designed so that under changes of ambient temperature, the movement of the latching surfaces 63 and 64 are substantially equal thereby providing proper ambient temperature compensation for the circuit breaker and permitting it to perform its circuit breaking function at the same current level or operating point, irrespective of wide changes in ambient temperature.

An adjusting means for the ambient temperature compensating means 80 is provided by an adjusting screw 98 that is fixed to the leg 82 of the bimetal member 81 and is also threadingly engaged with a vertical wall 99 of the circuit breaker housing 12. Movement of the screw 98 will move the latching surface 63 either to the left or right as viewed in FIG. 1 to set the operating point of the circuit breaker 10.

It is to be understood that the specific construction of the improved circuit breaker including an ambient temperature compensating means herein disclosed and described is presented for the purpose of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claims.

What is claimed is:

.1. An electric circuit breaker comprising a pair of separable contacts and an operating mechanism having a latch thereon releasable to effect separation of said contacts, a housing, said operating mechanism being mounted in said housing with an end thereof adjacent said latch being free to move to a limited degree transversely with respect to direction of operation of said operating mechanism, a current and ambient temperature responsive means affixed to said housing and having a transversely movable end with a latching surface engageable with the latch on said operating mechanism for moving said latching surface transversely with respect to the direction of said operating mechanism and out of engagement with said latch in response to a predetermined current, and an ambient temperature compensating means coupled to said housing and said end of said operating mechanism adjacent said latch for moving said end and said latch in the same direction as said end of said current and ambient temperature responsive means and said latching surface under changes in ambient temperature.

2. The combination of claim 1 in which said current and ambient temperature responsive means comprises a bimetal means positioned in said housing for moving said movable end thereof with said latching surface transversely with respect to the direction of movement of said operating mechanism as the result of changes in current or ambient temperature.

3. The combination of claim 2 in which said ambient temperature compensating means comprises a bimetal means having one end aflixed to said housing and the other end coupled to said end of said operating mechanism for moving said end of said operating mechanism in the same direction of movement as said movable end of said first-mentioned bimetal means as the result of changes in ambient temperature.

4. The combination of claim 3 in which the coefiicients of expansions of said first and said second bimetal members are selected to provide substantially equal movements of said latching surface and said latch under changes in ambient temperature.

5 6 5. The combination of claim 1 including means engag- References Cited ing said ambient temperature compensating means for UNITED STATES PATENTS providing an initial adjustment of said ambient temperatung compensating means Shaw 6. The combination of claim 3 including means engagr 23,78,557 4/1961 Ingwersen 200116 9 3,287,523 11/1966 MacDonald et a1. 200116 ing said bimetal means defined therein for providing an initial adjustment of said bimetal means and consequently an initial adjustment of said ambient temperature com- BERNARD GILHEANY Exammer' pensating means. R. COHRS, Assistant Examiner. 

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING A PAIR OF SEPARABLE CONTACTS AND AN OPERATING MECHANISM HAVING A LATCH THEREON RELEASABLE TO EFFECT SEPARATION OF SAID CONTACTS, A HOUSING, SAID OPERATING MECHANISM BEING MOUNTED IN SAID HOUSING WITH AN END THEREOF ADJACENT SAID LATCH BEING FREE TO MOVE TO A LIMITED DEGREE TRANSVERSELY WITH RESPECT TO DIRECTION OF OPERATION OF SAID OPERATING MECHANISM, A CURRENT AND AMBIENT TEMPERATURE RESPONSIVE MEANS AFFIXED TO SAID HOUSING AND HAVING A TRANSVERSELY MOVABLE END WITH A LATCHING SURFACE ENGAGEABLE WITH THE LATCH ON SAID OPERATING MECHANISM FOR MOVING SAID LATCHING SURFACE TRANSVERSELY WITH RESPECT TO THE DIRECTION OF SAID OPERATING MECHANISM SAID OUT OF ENGAGEMENT WITH SAID LATCH IN RESPONSE TO A PREDETERMINED CURRENT, AND AN AMBIENT TEMPERATURE COMPENSATING MEANS COUPLED TO SAID HOUSING AND SAID END OF SAID OPERATING MECHANISM ADJACENT SAID LATCH FOR MOVING SAID END AND SAID LATCH IN THE SAME DIRECTION AS SAID END OF SAID CURRENT AND AMBIENT TEMPERATURE RESPONSIVE MEANS AND SAID LATCHING SURFACE UNDER CHANGES IN AMBIENT TEMPERATURE. 